Many of the plants in nature, such as lotus, taro, and haulm leaves, exhibit the unusual wetting characteristic of superhydrophobicity. A superhydrophobic surface is one that can cause water droplets to bead off completely. Such surfaces exhibit water droplet with advancing contact angle of 150° or higher. In addition the contact angle hysteresis can be very low (the receding contact angle is within 5° of the advancing contact angle), producing a surface on which water droplets simply roll off. A self-cleaning surface results since the rolling water droplets remove dirt and debris. The lotus leaf accomplishes this effect through the use of a surface topography that present two different length scales to the outside environment. The surface of the lotus leaf for example, is textured with 3-10 micron-sized hills and valleys that are decorated with nanometer-sized particles of a hydrophobic wax like material. The hills and valleys insure that the surface contact area available to water is very low while the hydrophobic nanoparticles prevent penetration of water into the valleys. The net result is that water cannot wet the surface and therefore forms nearly spherical water droplets, leading to superhydrophobic surfaces.
Inspired by nature's self-cleaning superhydrophobic surfaces with contact angles (CA) larger than 150° and sliding angle<5° have attracted great interest over the last few years for both fundamental research and practical applications. For instance, they can be effectively used for textiles, traffic signs, hulls of ships, tubes or pipes, building glass, windshields of cars, satellite antenna, and conductors with a self cleaning surface. These surfaces usually have binary structures at both micrometer and nanometer scales, which makes it possible to trap a large amount of air and to minimize the real contact area between surface and water droplets. Reference may be made to Sun, T., et al. Angew. Chem., Int. Ed. 2004, 43, 1146; Feng, L., et al. Angew. Chem., Int. Ed. 2003, 42, 4217; Guo, Z., Zhou, F., Hao, J., Liu, W., J. Am. Chem. Soc. 2005, 127, 15670.
Superhydrophobic materials have high surface roughness which can be created by following certain techniques, one such example is Chemical Vapor Deposition (CVD). For example a technique for depositing thin layer of low surface energy materials is hot-filament chemical vapor deposition (HFCVD) which allows coating of objects with complex shape and nanoscale features. This technique can be used to deposit thin layers of a variety of polymers, including low surface energy polymers such as polytetrafluoroethylene. For further informations, see, e.g., United States Patent Application No. 2003/0138645 to Gleason et al.; K. K. S. Lau et al., “Hot-Wire Chemical Vapor Deposition (HECVD) of Fluorocarbon and Organosilicon Thin Films,” Thin Solid Films, 2001, 395, 288-291.
Other methods for surface roughening are based on lithographic techniques in which a mask with desired feature is formed over the material to be modified and then the material is etched through the space in the mask. For example the use of photolithographic technique to prepare rough surface, see e.g., Jai Ou et al, “Laminar drag reduction in microchannels using ultraphobic surfaces,” Physics of Fluids, Vol. 16, no. 12, December 2004.
The creation of hydrophobic sol-gel with high contact angles have been reported by the use of various organosilane compounds see, e.g., A. V. Rao et al., “Comparative studies on surface modifications of silica areogel based on various organosilane compounds of the type RnSiX4-n,” Journal of Non-crystalline Solids, 2004, 350, 216-223.
Synthetic superhydrophobic surfaces have been fabricated through various approaches. A superhydrophobic surface is a surface that has a water droplet advancing contact angle of 150° or higher and the receding contact angle is with in 5° of the advancing contact angle and very low sliding angle. Some of the general strategies employed for the formation of CNT based superhydrophobic surfaces involve aligned CNT which were prepared through sophisticated techniques like plasma enhanced chemical vapor deposition and carbon nanofiber based superhydrophobic surfaces prepared by pyrolysis method. Reference may be made to Li, S., et al. J. Phys. Chem. B 2002, 106, 9274; Liu, H., et al. Angew. Chem. Int. Ed. 2004, 43, 1146; Lau, K. K. S., et al. Nano Lett. 2003, 3, 1701; Huang, L., et al. J. Phys. Chem. B. 2005, 109, 7746; Feng, L., et al. Angew. Chem., Int. Ed. 2003, 42, 4217; Zhu, Y., et al. Chem Phys Chem 2006, 7, 336.
Surfaces which show superhydrophobic nature with corrosive liquids such as acidic and basic solutions are very important but rare, only few reports pertaining to this aspect is known in literature. Most of the superhydrophobic surface is demonstrated with pure water. It is essential to prepare superhydrophobic surfaces which have little or no effect due to the change in the pH environment. Reference may be made to Feng, L., et al. Angew. Chem., Int. Ed. 2003, 42, 4217; Guo, Z., Zhou, F., Hao, J., Liu, W., J. Am. Chem. Soc. 2005, 127, 15670.
One specific example for creating medical devices which have reduced resistance to movement of adjacent materials, including both fluid flow and solids can be seen in USPA: 2007/0005024. One specific example for micro fluidic device useful in industries for creating channels with predictable and optimal level of fluid flow resistance can be seen in U.S. Pat. No. 6,923,216. One specific example for creating superhydrophobic surfaces using silicon nanofibre constructed by gold colloid initiated chemical vapor deposition process, in that fluorinated nanowire surfaces have high contact angle, Reference may be made to US: 2005/0181195.
Synthetic procedures to construct individual nanostructures on surfaces and in bulk are described for “Single-Walled Carbon Nanotubes,” Chem. Phys. Lett. 1998, 292, 567-574. Of course, the current invention is preferably done using different method of construction but the material used etc. may overlap.
Superhydrophobic surfaces with CNT based composites are important because the field of CNT has created broad interest and numerous theoretical and experimental studies which reveal interesting chemical and physical properties for CNT based materials. They find application in organic light emitting diodes, optoelectronic and photovoltaic devices, sensors, field-emission device, logic gates, probes in chemistry and biology. It has been shown that the composite of π-conjugated molecules and CNT have promises for application in photovoltaic device, OLED, solar cells owing to the novel electronic interaction between these two elements. Reference may be made to Guldi, D. M., Rahman, G. M. A., Zerbetto, F., Prato, M., Acc. Chem. Res. 2005, 38, 871; Rahman G. M. A., et al. J. Am. Chem. Soc. 2005, 127, 10051; Ago, H., Petritsch, K., Shaffer, M. S. P., Windle, A. H., Friend, R. H., Adv. Mater. 1999, 11, 1281.
Accordingly this invention deals with Formula 1, which is an oligomer of poly(p-phenylenevinylene) polymer, the interaction of Formula 1 with carbon nanotubes are unknown and also invention deals with the creation of superhydrophobic coatings using nanocomposite material.
Oligo(p-phenylenevinylene) derivatives are known to form self-assembled structures under different conditions, reference can be made to A. Ajayaghosh et al., J. Am. Chem. Soc. 2001, 123, 5148-5149., and A. Ajayaghosh et al., Angew. Chem. Int. Ed. 2006, 45, 1141. Interaction of conjugated polymers with carbon nanotubes and their characterization can be seen through the following references, A. Star et al., Adv. Mater. 2001, 13, 899, and S. Curran et al., Syn. Met. 1999, 103, 2559.
Despite the above informations, a simple and viable solution processable carbon nanotube based superhydrophobic coating is not known.